Liquid crystal displays (LCDs) are commonly employed in mobile telephones to display information to the user. An LCD typically comprises liquid crystal composites disposed between upper and lower substrates. Display elements are formed by etching a conductive film deposit on the inner surface of each substrate. Etched areas become the display background, unetched areas become the display elements. When a voltage potential is applied, the display elements become visible.
Numerous methods have been used in the past to connect the electrical contact points on the LCD with the contact points on a printed circuit board or other electrical circuit. One such method is to directly solder conductive leads extending from the LCD to the circuit board. This approach, however, has several drawbacks. The LCD is fragile and stiff soldered leads can break the glass upon impact. The use of soldered contacts also necessitates an extra soldering process on the assembly line. Finally, it is difficult to remove or replace the LCD after it has been soldered in place.
Another approach which has been employed in the past is to use an elastomeric connection (i.e., zebra strip) to connect the LCD to the printed circuit board. An elastomeric connection typically comprises a strip of elastomer material having embedded contacts. A guide is used to hold the elastomeric strip which is compressed between the LCD and the printed circuit board. This approach also has several limitations. First, elastomers have a practical aspect ratio limit that causes connections to be unreliable if that limit is exceeded. Second, this connection method requires careful attention to counter-balancing the elastomer compression to prevent continuous stress on the LCD glass. Cleanliness of the parts is also critical to this design. Finally, this approach works best only when the LCD contacts are on the back side of the LCD (i.e., facing the printed circuit board). If the contacts are on the top side of the LCD glass, then an elastomeric connector is very difficult to implement. In this case, the elastomer would have to wrap around to the top side of the glass and would require that compression be maintained on the top side of the LCD, as well as between the LCD and printed circuit board.
A third approach which has been used in the past is an elastomer and connector block combination. This type of connector system typically comprises a C-shaped connector block clipped and glued to the LCD with an elastomer connecting the block to the printed circuit board. One problem with this approach is that the connector block can be easily shifted due to insufficient adhesion to the LCD glass and cannot be placed with tight tolerances. In addition, the connector block and elastomer combination relies on an additional contact interface presenting more opportunities for defects. The signal must pass from the printed circuit board to the elastomer, from the elastomer to the connector block, and from the connector block to the LCD. This extra interface is also a source of an additional layer of tolerances. This design also adds costs due to the use of two connectors.
A fourth approach to the problem of connecting an LCD to a printed circuit board is to use a flex-film. Two types of flex-film connections are generally used--soldered/heat-sealed connections and zero insertion force (ZIF) connectors. In both instances, a flex-film is permanently attached to the LCD and the tail of the flex-film is connected to the printed circuit board, either permanently via soldering or heat-sealing, or preferably through a ZIF connector mounted on the printed circuit board. One problem associated with flex-film is that it sometimes entails tedious routing of the flex-film during the assembly process. While the soldering and heat-sealing can be implemented on automated assembly lines, this requires additional equipment and processing. Flex-films employing ZIF connectors usually cannot be automated. ZIF connectors also introduce an extra contact interface which represents additional opportunity for defects in production. The signal must pass from the printed circuit board to the ZIF connector, from the ZIF connector to the flex-film, and from the flex-film to the LCD. This extra contact interface is also a source of an additional layer of tolerances. This method also adds costs due to additional parts.
Accordingly, there is a need for a new type of LCD connection system to enable connections to be quickly and easily made between an LCD and a printed circuit board where the contacts are disposed on an upwardly facing surface of the LCD.